Question

find the sum of all integers between 100 and 1000 which is divisible by 7

Answer 1

$a = 105 \: t2 = 112 \\ d = 7 \\ tn = 994 \\ tn = a +( n - 1) \times d \\ 994 = 105 + (n - 1) \times 7 \\ 994 = 105 + 7n - 7 \\ 994 = 98 + 7n \\ 7n = 994 - 98 \\ 7n = 896 \\ n = \frac{896}{7} \\ n = 128 \\ sn = \frac{n}{2} \times (t1 + tn) \\ s128 = \frac{128}{2} \times (105 + 994) \\ s128 = 64 \times 1099 \\ s128 = 70336 \\hope \: it \: will \: help \: u \: \: \\ plz \: mark \: as \: brainelist....$